English

Abstract

The treatment of acidic coal pile runoff (CPR) using an alternative constructed wetland design was evaluated. This alternative design, which provided improved wetland performance, was based on the partial re-circulation of treated water into a detention basin located immediately upstream from a Reducing and Alkalinity Producing System (RAPS). This modification created a semi-passive RAPS-based system we refer to as a Recirculating RAPS (ReRAPS). Previous work suggested that this wetland, utilizing the ReRAPS modification, could dampen the effects of intermittent, or shock, loading usually associated with CPR and still achieve desired effluent contaminant concentrations. The purpose of this study was to confirm the previous results through more frequent chemical and hydrological monitoring. The ReRAPS was monitored during 41 days of CPR treatment, which included four storm events during January through March 2001. The CPR contained an average iron concentration of 12.8 mg/L, 24.8 mg/L of aluminum, 2.9 mg/L of manganese, and 178.0 mg/L of acidity. The detention pond removed 82% of the total iron, 59% of the aluminum, and 35% of the acidity loading prior to the RAPS component. Manganese behaved conservatively in the detention pond. Average concentrations at the wetland discharge for total iron, aluminum and manganese were less than 0.20 mg/L. The 2001 wetland monitoring has confirmed that the ReRAPS modification enhances the basic RAPS wetland design by moderating the pH of contaminated water and reducing the contaminant loading prior to the RAPS component.